I then... roll the fabric over the foam... I'm making all of this sound easier than it is.

The difficulty I had turning the first version of the shoulder straps right side out after sewing and then stuffing the foam is the reason I decided to sew with the right side out and then hide the seams with grosgrain. Even with this method, it still took me over two hours just to stuff in the foam for the hip belt. I wish I'd thought of rolling the fabric onto the foam. I think I'll stick with sewing right side out, though, for two reasons. 1) I really like the look of the grosgrain edging, and 2) I think the taper of the hip belt will make the next one a lot easier to stuff.

I'm going to take your advice about sewing the webbing on and sewing through to lock it all together. I think my machine should be able to do it with the foot raised if I turn it by hand.

The flat side is the part that goes against my back. I was worried it wouldn't have enough volume for my gear, so I figured I'd make it as close to a cylinder as possible, given the flat side, because a cylinder has a large volume compared to it's surface area (the amount of fabric). I actually used 3d modeling software to estimate the volume, and if I leave the top open, it's right at 50L. Of course, it'll be a bit less with the top rolled closed, but I'll add an extension collar. I actually wrote a tiny little program to crunch the numbers and come up with the correct radius for the partial circle, given the dimensions of the bag and the width of the frame sheet. I think it worked out really well.

With the new bottom in, it stands upright on it's own.

ETA: In order to sew everything on/in (straps, belt, pockets, and frame) I'll have to cut down the side of the bag vertically and sew it back together when everything else is done. But, I don't think the bottom will be in the way.

It's been a long time since I posted on this project, because you know, life happens. I'm using plywood as a frame. I'd tried to add lightening holes manually with a spade bit, but it tore up the wood pretty badly, and I decided to start over with another piece. Well it just so happens I have a friend with access to a laser cutter, and he let me use it. Without further ado...Even with so much material removed, it's still nice and stiff. I can bend it a bit by hand, but I think it will work nicely in the backpack. It's still surprisingly heavy though! I don't have a very precise scale, but I would hazard a guess at around 8oz. It'll just have to work though. The next step is to make it reasonably water resistant somehow. I'm thinking polyurethane. I think I've still got an old can in storage somewhere, but who knows if it's still any good?

My first internal frame was bought from a small manufacturer in Chico, Ca called Caribou Mountaineering. It had a huge single bag and a web system to lash on tools on the outside. The supports were 2 strips of African Basswood, roughly 1 1/2"x 1/4" which would bend but not break. I think it's the only pack I've seen which used wood supports. The strips were fitted into 2 4" sleeves top and bottom and you could remove the strips if you needed to. I gave it to a friend and it still sees a trip a year or so, after nearly 40 years. Is your plywood going on the inside of your bag? Most grades of plywood over time, with stress and drying, will de-laminate unless its marine grade. Don't mind me, I'm just a regular old carpenter. That laser cutting is impressive.

Bluefish, yes it will go on the inside. That's too bad about the delaminating. Unfortunately it's not marine grade (that stuff is expensive!). I'm starting to think I should have gone with a metal or composite frame, but I don't want to spend any more money at this point. If it's just going to break down anyway, I might as well just throw it in there untreated. It should be fairly protected in the bag anyway and hopefully last long enough to evaluate the design. Thanks for the professional input.

Oh, and regarding the laser cutting, I was rather pleased with it myself. It's too bad it'll be hidden away. I think if I were to do it again, I'd make the walls between the hexagonal cells thinner and maybe the strips at the top and bottom less wide as well. It could stand to go on a diet. If that made it too flexible, I'd put a couple of reinforcing strips on it like an I-beam. This took about 1.5 - 2 hours to cut though, so I'm not going to bother my friend with it. I'll just deal with the extra few ounces.

I know I said I was going to leave the frame as-is, but the more I thought about how heavy it is, the more it bothered me. I finally took it to the post office and got it weighed. 11.8oz! I'm definitely going to shave this thing down some more.

It's been almost 9 months since I worked on this project, but I'm back to it now. I've revamped the hip belt. Before, there was a big gap between my back and the top of the belt, rather than hugging my lumbar. I brainstormed different ways to fix this, but in the end, it was very simple. I just cut the belt in half, angled the edges where the two pieces would form a V, and sewed them back together. This effectively removes the extra material that was causing it to gap in the back. It feels much more snug and secure now.

I hate to do this too you but are you putting a back pad at the illac crest of your back ( the bit that curves towards your ass) ? That may interfere with the hipbelt snug fit ? If you think about it when you walk the rucksack is going forward and thrusting down your lead leg by driving into your back. If you get good contact you get good load transfer. Alot of the best light bags ( exped lightening ) do not skimp on the padding only on the rest of the bag.

I like the plywood frame shame its so heavy, a couple of aluminium stakes only weigh 4 oz. What alot of companies do is have a stiff foam back, sometimes reinforced with thin steel rods.

Petro, I'm not really sure I understand the question, but the only padding is in the hipbelt itself, none on the pack. The belt will be sewn directly to the pack.

For the frame, I've switched to bamboo skewers. It was $0.88 for a whole package, so I couldn't resist trying it out. I'm gluing together three for each vertical support (cut to two feet) and three for the top horizontal piece (cut to a foot). I'll report how it works after it's all put together.

For weight, I'd carry an absolute max of 40lbs. I've carried low to mid 30s in the past, but I'm looking to reduce this. I'm switching from an oversized tent to a "polycryo" tarp when it's not too buggy, and of course, the pack itself will be much lighter.

They usually do a lumbar pad which is a wedge of foam in the middle of the hipbelt as you probably know, the wedge is usually thicker at the bottom than at the top to transfer the weight into the back.

I think I see what you mean. With the way the belt fits snuggly against my lumbar region after the last modification, I'm hoping that won't be necessary. However, if it is, I should be able to add a lumbar pad after the fact. The shape of the hip belt is an amalgam. I started with the G5 belt. The V came about initially from thinking about adding two separate darts to take in the slack, and then from reading about how the McHale hip belts form a V in both the front and the back. That's when I realized that adding a single dart in the back, or cutting off the extra altogether and reattaching it into the V shape is essentially the same thing.